The overall goal of this P01 is to develop and evaluate approaches for liver-directed gene therapy for ornithine transcarbamylase deficiency (OTCD) that are based on treatment of the acute hyperammonemic crisis by transient expression of OTC, and long-term prevention of hyperammonemia by stable correction of OTCD. OTCD is well suited for the development of gene therapy: Current treatment has failed to avert a high mortality or morbidity rate; Given the relative frequency of OTCD, an adequate population is available for study; The OTC gene has been sequenced and preliminary studies of gene therapy in animal models have been promising; The OTC gene is not rate-limiting for ureagenesis, so excessive activity should not have adverse consequences; and Restoration of enzyme activity in the liver, should suffice to normalize metabolism without the need to introduce the gene into the central nervous system. The grant consists of three projects and four cores. Project I seeks to define the molecular basis for the current limitations of in vivo gene therapy using first generation recombinant adenoviruses in liver, which include transient expression of the transduced gene and the development of inflammation at the site of transgene expression; to develop second generation recombinant adenoviruses expressing OTC in which essential genes other than E1 have been inactivated; to analyze these improved recombinant adenoviruses in vitro and in vivo; and to develop methods for efficiently transducing functional OTC genes into primary cultures of human heepatocytes using recombinant retroviruses. Project II focuses on two murine models of OTCD, the Spf and Spf/ash mouse. The specific aims are to study the efficacy of in vivo gene therapy in correcting the metabolic and neurochemical and behavioral consequences of OTCD in the adult and neonatal animal. Project III focuses on using recombinant adenoviruses and retroviruses to treat OTCD in humans. We hypothesize that a recombinant adenovirus containing the OTC gene will be effective and safe for the short-term treatment of neonates and older children with OTCD who are in hyperammonemic crisis. We further hypothesize that long-term correction of OTCD can be achieved either by ex vivo or in vivo gene therapy using a recombinant retrovirus or a second generation recombinant adenovirus. Finally, we hypothesize that a cellular immune response following gene therapy may affect safety, efficacy and duration of gene therapy. The cores that support these projects include an Administrative Core, a Recombinant Viruses Core (containing a Vector development laboratory and a Human Applications Laboratory), a Toxicology Core (containing an Animal Models program and a Cell Morphology Laboratory), and a Mass Spectroscopy Core to perform stable isotope studies of urea turnover.